Hi there, being in the industry, yes, R134a does have a phase out date, as do most of the refrigerants we use today. R22 was phased out long ago, but still remains available. This phaseout date can mean a lot of things, but for simplicity here we go:
*Basically, no NEW equipment will be able to be built containing this compound.
*No NEW refrigerant will be made.
*Once Phased out, cost is usually driven higher by market conditions.
However, since ALL refrigerant is required to be recovered, it will be available as "reclaimed" (think re-manufactured, or cleaned-up used).
Also, not all countries have adhered to the various protocols, so "boot-leg" refrigerant is also available. Be warned, many are not what they claim (imagine that, con artist and crooks) and are petroleum based.
For my money, go R404a, while R134a has a 2030 phaseout date, the only date for R404a is under the more general HFC phase out (EU).
This is an ever changing reality in our trade, and its no fun, When I ran service I had just a handful of refrigerants to worry about, now there are hundreds, many of which you may never see again, or at all.
However, all this is really a moot point....no one would do a repair on even a 10 year old air drier, they are like refrigerators these days, disposable.